The present invention relates to a power converter as well as the manufacture of a power converter.
Power converters of the type cited here are configured in greatly varying embodiments. They are used for converting or controlling electrical power. Power converters may be implemented as rectifiers, inverters, DC converters, and AC converters. Corresponding to these embodiments, the power converters have power converter valves, particularly diodes, thyristors, transistors, MOSFETs, IGBTs, and Triacs. Therefore, there are many types of controllable and non-controllable power converter valves. In the field of motor vehicles, power converters are used in particular as rectifiers which convert a periodic quantity provided by a generator into a zero-frequency quantity. Three-phase generators which provide multiple AC voltages phase-shifted in relation to one another are mainly used. The rectifier must correspondingly be implemented as a multipolar rectifier. These types of rectifiers have a corresponding number of individual, discrete power diodes which form the rectifier assembly. The rectifier assembly includes two terminal plates, one of which forms the positive voltage terminal and the other of which forms the negative voltage terminal. Both terminals are electrically insulated in relation to one another. The diodes and their housings may be pressed into the plates. As a rule, the negative terminal plate is attached to the end shield of the generator to produce a thermal and electrical contact. The positive terminal has a pin in order to be able to tap the voltage. This positive terminal is implemented as a heat sink in order to cool it. It may be situated in the airflow of the generator fan or also be thermally coupled to the end shield of the generator using a heat conducting film.
For the thermal conception of a single press-in diode and of the complete rectifier, two different operating cases must be considered. In normal operation, with an approximately constant load of the generator, a few tens of watts of power loss arise in the current path of each diode, which must be dissipated as heat via the negative and/or positive terminal(s). The second, load-dump case occurs in the event of sudden load shedding, after which the generator regulator requires a certain period of time in order to adjust the current of the exciter winding and regulate the generator voltage. In order to avoid high voltage peaks in the vehicle""s electrical system during this period, the rectifier diodes may be implemented as Zener diodes, which are capable of absorbing the entire output of the generator for a short time.
The power losses arising in this case may be of the magnitude of multiple kilowatts. The heat then arising on the rectifier diodes cannot be dissipated via the heat sink, but rather is collected in the diode housing itself through an adequately dimensioned copper mass, which is therefore used as a heat buffer. Therefore, the power converters have been shown to be costly to construct and, in addition, relatively large, sincexe2x80x94for a three-phase bridge rectifierxe2x80x94six individual diodes must be cooled using terminal plates having complicated constructions. In addition, a higher wiring outlay results for connecting the individual diodes and for electrically connecting the power converter to the electrical machine, for example, a generator.
In contrast, a power converter of an example embodiment of the present invention provides a significant simplification of the construction as well as a reduction of the necessary space of the power converter, and a significant reduction in cost for its manufacture. In particular, thermal coupling is achieved between the two mounting plates, because the mounting plates used as an electrical terminal and the semiconductor substrates form a stack and a thermally and electrically conductive insert is positioned between the semiconductor substrates, which allows the electrical connection. It is therefore sufficient if one of the mounting plates is situated on a separate heat sink, for example on a generator end shield, using its attachment arrangement, in order to be able to dissipate the heat loss. A heat flow therefore results from the semiconductor substrate positioned near the one (upper) mounting plate to the other (lower) mounting plate, via the semiconductor substrate and the insert lying between them. Through the stacked arrangement of the semiconductor substrates between the mounting plates, both mounting plates are additionally electrically insulated in relation to one another, so that no further components or measures are necessary for this purpose. It has been shown that an additional heat sink for one of the mounting plates may be eliminated. Particularly for three-phase bridge power converters, the plus and minus terminals may be implemented on one of the mounting plates as a joint conductor bus above or below, respectively, the power converter valves and, in addition, additional wiring may be largely eliminated, since the insert arranged between the power converter valves is used as a terminal on the three-phase side.
The present invention is not restricted to rectifiers for use in three-phase generators. All other types of power converters may be implemented using it. If, for example, the insert is implemented as bipolar and the semiconductor substrate has two contact surfaces on its surface facing the insert, controllable power converter valves, particularly thyristors and transistors, MOSFETs, and IGBTs may also be used. The power converter according to the present invention is therefore usable in many electrical power conversion and control fields.
In order to implement the thermal and electrical conductivity of the mounting plates, in an example embodiment they may be produced from copper or at least include copper. They may be implemented in a plate shape, a flat surface particularly being provided in the mounting plate having the attachment arrangement, in order to provide a large thermal transfer surface to the end shield of the generator, so that the heat generated may be properly dissipated to the generator housing. Of course, it is also possible not to attach the power converter directly to the generator, but to another element used as a heat sink.
If the power converter is attached to the end shield of an electrical machine, particularly a generator, additional advantages result for the design of the machine: Due to the low overall dimensions of the power converter, enlarged air intake openings may be implemented on a housing, through which either the cooling, and therefore the efficiency of the machine, or the fan impeller of the machine, may be reduced in order to reduce the emission of noise. The power converter may also be attached to a liquid-cooled machine. Furthermore, high flexibility of the arrangement on a machine results due to the low overall dimensions of the power converter. The power converter may be arranged on a claw-pole machine, particularly a claw-pole generator of a motor vehicle, on the A or B side. Due to the small dimensions of the compact power converter, higher mechanical stability in relation to shock and vibration stresses also results, so that high and durable functional reliability is provided, particularly during its use in the motor vehicle.
A power converter, particularly of the type described above, may be manufactured easily and cost-effectively. During manufacturing, the components are layered on one another, an electrically conductive contact arrangement is applied in at least some regions between the components. During the layering of the components (mounting plates, semiconductor substrates, and insert) on one another, they May be laid on top of one another in sequence, the contact arrangement being provided between each of them. However, it is also possible for partial assemblies to be premanufactured. Thus, for example, it is possible to attach one of the semiconductor substrates onto each mounting plate using the contact arrangement. Both mounting plates are then assembled together, enclosing the insert, and connected to one another using the contact arrangement. The sequence may therefore be selected almost arbitrarily, the stacked arrangement of the components, however, always being selected.
In one exemplary embodiment, the contact arrangement may be a soldering paste or soldering foil. The soldering paste is applied onto at least one of the components which are to be joined. When using soldering paste, the paste may produce a certain adhesive effect, so that the parts lying on one another adhere to one another and therefore cannot slip in a subsequent heating process during assembly and are connected to one another in a precise alignment.
However, it is also possible to produce the contact arrangement through diffusion soldering or conductive gluing. For conductive gluing, for example, an adhesive may be used which is partially electrically conductive, i.e., the paste may contain electrically conductive particles.
In order to ease the joining of the components during preassembly, an electrically non-conductive spacer may be placed between the mounting plates. This spacer may be implemented such that an essentially closed housing is formed, in which the housing walls are formed by the mounting plates and the spacer. This spacer may be implemented as a partial assembly with the insert. The spacer may also be removed after the connection of the components to the contact arrangement. However, it may also remain in position until the free space existing between the mounting plates is filled up using a filling compound or injected using plastic. However, it may also remain after the free spaces between the mounting plates are filled up.
Particularly in multipolar power converters, in which multiple semiconductor stacks therefore lie next to one another, the inserts lying between two semiconductor substrates may be connected to one another. Terminal lugs which project over the edge of the housing may be provided. The lugs may be connected to one another at their ends. In this way, the assembly of the power converter is simplified. After the assembly is completed, the inserts, particularly their terminal lugs, may be separated from one another mechanically.
The components are pre-fixed, in particular during preassembly. For this purpose, pins or recesses may be used, for example, on the facing sides of the terminal plates, which work together with pins or recesses used on the spacer wherein the pins engage in the recesses. The spacer may thus additionally be used as a pre-fixing element, whichxe2x80x94as described abovexe2x80x94may be removed after assembly.
Ifxe2x80x94as just describedxe2x80x94the free spaces are filled or injected, the lateral edges of the semiconductor substrate may be painted using a protective paint in order to protect the substrate from moisture and the filling compounds and/or plastics, which may be chemically aggressive.